CN1071716C - Process for preparing pure alkali and/or ammonium tungstate solutions - Google Patents

Abstract

The present invention relates to a kind of method that prepares pure alkali metal tungstate and/or ammonium tungstate solution from polluted alkaline tungstate solution, and above-mentioned polluted tungstate solution especially refers to the method that is contaminated with silicon, phosphorus, Solutions contaminated with arsenic, tin, antimony, vanadium, tantalum, niobium, titanium and molybdenum. Acidification of the contaminated solution to form a precipitate without the addition of precipitants or precipitation aids, which is then filtered.

Description

Method for preparing soda metal tungstate and/or ammonium tungstate solution

The present invention relates to a kind of method that prepares soda alkali metal tungstate and/or ammonium tungstate solution from polluted alkaline tungstate solution, and above-mentioned polluted tungstate solution especially refers to silicon, phosphorus, arsenic , tin, antimony, vanadium, tantalum, niobium, titanium and molybdenum contaminated solution, where the contaminated solution is acidified to form a precipitate without the addition of precipitants or precipitation aids, and then the precipitate to filter.

The raw materials used to obtain tungsten, especially tungsten ore, often contain small amounts of molybdenum and arsenic. It is often required that the content of Mo and As in ammonium metatungstate and powdered metal tungsten products should be very small. However, tungsten raw materials with a molybdenum content of more than 2% by weight of tungsten have entered the market in large quantities.

Tungsten-containing solutions from various leaching processes are often contaminated with a number of different elements, depending on the raw materials used. In addition to molybdenum, frequently occurring impurities are phosphorus, arsenic, silicon, aluminum, vanadium, titanium, niobium and tantalum. So far, many methods for separating these impurities have been disclosed, which include adjusting the pH value of the above-mentioned strong alkaline tungstate solution to 8- Between 11. However, this precipitation process cannot be carried out quantitatively, especially since most of the arsenic remains in solution (see Tungsten Symposium (Tungsten Symposium), San Francisco, June 1982, p. 77, Table 2).

Currently, the most common method for separating molybdenum from tungstate solutions is to precipitate MoS ₃ from previously purified tungstate solutions (see Gmelin, Wolfram, System Nr.54, Ergnzungsband Al (1979) , pp. 44-46). After pre-precipitation of silicon, phosphorus, aluminum and other elements, the tungstate solution from the alkaline leaching process was treated with NaHS at pH 8-10, and after the formation of MoS ₄ ^2- was treated with H ₂ SO ₄ precipitates as MoS ₃ at pH 2-3. Usually the content of molybdenum in the precipitate is basically the same as that of tungsten, and contains a considerable amount of free sulfur and arsenic.

Such deposits are of little use, therefore they must often be disposed of as special waste. In addition, only mineral acids can be used to adjust the pH of the solution, resulting in a large amount of neutral salts.

Mintek Report No. M226 (1985.11.25) describes a method for separating MoS42- in solution with an OH ^- type solid ion exchanger. The disadvantages of this method are the low adsorption capacity of the ion exchanger for Mo, the low degree of separation of molybdenum from tungsten, and the presence of arsenic in the precipitated _MoS3 .

According to US-4288413, molybdenum can be isolated in the form of MoS ₄ ^2- by extraction with quaternary ammonium compounds at a pH value of 7-9.

Because when extracting arsenic under the above conditions, arsenic and tungsten can be separated, but arsenic and molybdenum cannot be separated. Since MoS ₄ ^2- can only be back-extracted by means of an oxidant such as H ₂ O ₂ or NaOCl, it cannot be separated from the co-extracted tungsten, thus increasing the loss of W. The resulting product is a mixture of sodium molybdate and sodium tungstate, which is difficult to use further and is also doped with arsenic.

A procedure for avoiding arsenic contamination is disclosed in DE-C19500057, but this patent does not mention the problem of molybdenum contamination in tungstate solutions.

The object of the present invention is to provide a method for selectively removing impurities in a tungstate solution while minimizing the amount of waste, especially special waste. The method can obtain economical and applicable molybdenum products from molybdenum-containing raw materials.

The above objects of the present invention are achieved by combining a precipitation process with two anion exchange processes.

The invention provides a method for preparing soda alkali metal tungstate and/or ammonium tungstate solution from contaminated alkaline tungstate solution, especially the contaminated solution is contaminated with silicon, phosphorus, arsenic, tin, Tungstate solution contaminated with antimony, vanadium, tantalum, niobium, titanium and molybdenum, wherein the solution is acidified, precipitated without the addition of precipitants or precipitation aids, and the resulting precipitate is filtered off, characterized by the above process When the acidification process is carried out until the pH value of the solution is 7-10, a large amount of impurities other than molybdenum and arsenic ions are precipitated and filtered out, and a weakly alkaline to medium alkaline ion exchanger is used to separate from the filtrate, including Arsenic but other impurities except molybdenum ions, the filtrate is treated with sulfide to generate thiomolybdate, and thiomolybdate is separated by using a sulfide-type solid or liquid ion exchanger, thereby obtaining soda metal tungsten salt and/or ammonium tungstate solution.

Preferably using one or more mineral acids, CO ₂ and/or membrane electrolysis, the solution is acidified to a pH of 7-10, preferably adjusted to a pH of 8-8.5. This will inevitably lead to precipitation. This precipitation takes place without the addition of precipitating agents or precipitation aids. After filtration, the first step of ion exchange is performed with a weakly to moderately basic ion exchanger. Preference is given to using weakly to moderately basic ion exchangers of the solid OH type, ie ion exchangers which mainly contain quaternary ammonium groups as active components. The ion exchange method separates arsenic, phosphorus, silicon, vanadium, titanium, niobium and tantalum impurities better than any known precipitation method. This method is especially useful for isolating arsenic, which remains in solution if precipitation is used. The eluate obtained by regenerating the ion exchanger contains the above-mentioned impurities concentrated 10 times, so the impurities can be precipitated out in a relatively short period of time with a small amount of chemical reagents. The concentration process can also precipitate arsenic. It is advantageous to recycle the remaining WO ₄ ^2- containing solution upstream of the first ion exchange process.

In the course of tests with commercially available ion exchangers, it has surprisingly been shown that the conversion of an anion exchanger of the OH form to an ion exchanger of the sulfide form significantly increases the molybdenum adsorption capacity and selectivity. In particular weakly basic anion exchangers (eg Lewatit MP 62 sold by Bayer AG). Although Mo can be separated with moderately to strongly basic anion exchangers, Mo is more and more difficult to elute as the basicity increases. The H ₂ S gas used to form the ion exchanger can be recycled in large quantities, and in the acidification process after ion exchange, the H ₂ S gas is recovered with water in the gas scrubber and then used in the next cycle to form the ion exchanger. By acidifying the eluate from the second ion exchange step, pure _MoS3 low in arsenic was precipitated.

Alkaline solutions from various leaching processes (eg high pressure leaching, melting, calcination) are preferably treated with the method of the invention, preferably to adjust the tungsten content to 80-100 g/l. After the above-mentioned precipitation of impurities by acidification, in order to separate the remaining impurities as well as arsenic and phosphorus after precipitation, it is preferable to perform ion exchange with a weakly basic anion exchanger. The solution previously purified in this way is then treated with 3-5 times the stoichiometric amount of sulfide, based on molybdenum, in order to form thiomolybdate. The sulfide used here is preferably H ₂ S, NaHS, Na ₂ S, (NH ₄ ) ₂ S or an organic compound that can release sulfide. Stir the solution for several hours, preferably 4-10 hours, preferably at elevated temperature, preferably at 50-95°C, and adjust the pH of the solution to 8-8.5, preferably with mineral acid or _CO2 . The solution is then passed upwards through an ion exchange column packed with a weak base anion exchanger, which has been pretreated with _H2S /water to a pH <7, thereby converting the exchanger to ^{S2 -type} exchanger.

Breakthrough begins when the adsorption capacity of the exchanger is reached. Then the feeding process was stopped, and the exchange column was washed until there was basically no tungsten in the washing liquid, and then eluted with dilute sodium hydroxide solution. Then wash the exchange column with water.

The column is preferably eluted and washed downwards. The eluted exchanger is then reshaped to a pH <7 with _H2S /water from the tail gas scrubber, thus ready for the next cycle.

The purified tungstate solution can be further acidified with mineral acid, _CO2 or membrane electrolysis and further processed by known methods. After extraction is applied, the tungsten-containing solution can be further processed into ammonium metatungstate.

Preferably, the pH value of the molybdenum-containing eluent is adjusted to 2-3 with a basic organic acid, and then the molybdenum is precipitated into MoS ₃ . Since the arsenic had previously been removed from the tungsten-containing solution by ion exchange in the first step, pure MoS ₃ was now produced, a product containing only a small amount of tungsten that could be used in molybdenum metallurgy.

The H ₂ S gas generated during the acidification of the tungstate solution and the eluent is absorbed with water, preferably in a gas scrubber, and used to form the anion exchanger.

The content of the present invention is described below by examples, but these examples do not limit the present invention.

Example

1. OH type Lewatit MP 62

(weakly basic anion exchanger mainly containing ternary exchange groups - sold by Bayer AG)

Exchange column: 300ml OH type Lewatit MP 62

Initial solution: 85.0 g/l of tungsten in 11 liters of solution

Molybdenum 1.97g/1 (=2.3% Mo, based on W)

                                        

The solution was passed up through the column at a rate of 0.5 bed volume per hour (150 ml/h).

Effluent: 84.1g/l tungsten in 11 liters of solution

Molybdenum 26mg/l (= 309ppm Mo in W)

pH 8.5

Wash the ion exchanger with about 0.51 H ₂ O to remove W, elute the exchanger down with 0.51 NaOH (100g/l) at a rate of 1BV/h, and then wash with H ₂ O to a pH of 8 (approx. liters of wash water) (BV = bed volume).

Eluent: tungsten 8.7g/l in 1 liter solution

Molybdenum 19.04g/l

0.5 L of the eluate was adjusted to pH 2 with 35 mL of semi-concentrated H ₂ SO ₄ and stirred at 70° C. for about 3 hours, and the precipitate was filtered, washed and dried.

Precipitate: 24.3 grams of precipitate containing molybdenum 35.9%

Tungsten 1.35% filtrate: 500ml solution contains tungsten 8.22g/l

Molybdenum 0.047g/l

2. S ^2- Type Lewatit MP 62

Exchange column: 300ml S2 ^- type Lewatit MP 62

Initial solution: 12 liters of solution containing tungsten 80.9g/l

Molybdenum 1.92g/l (=2.3% Mo, based on W)

pH 8.0

The solution was passed up through the column at a rate of 0.5 bed volume per hour (150 ml/h).

Effluent: 79.3g/l tungsten in 12 liters of solution

Molybdenum 6.7mg/l (= 84ppm Mo in W)

pH 8.4

Wash the ion exchanger with water and elute the ion exchanger:

Eluent: 13.1g/1 tungsten in 1 liter solution

Molybdenum 23.9g/l

The sum of the molybdenum content of the effluent and eluent was slightly higher than that of the initial solution because an additional 3 liters of solution passed through the exchange bed, but the exchange bed broke through after 12 liters.

0.5 liters of eluate is processed as shown in Example 1:

Precipitate: 27.5 grams of precipitate containing molybdenum 39.1%

Tungsten 2.65%

Filtrate: 600ml solution contains tungsten 8.86g/l

Molybdenum 0.46g/l

pH 1.74

3. Comparison of the quality of precipitated _MoS3 with and without pre-separated arsenic

Initial solution: W 70g/l

Mo 1.2g/l

As 13mg/l

pH 8.3

3.1 Comparative example: only utilize the OH type Lewatit MP 62 of embodiment 1 to separate Mo, and the technological status is: Mintek Rep.no.226

Recycled MoS ₃ : Mo 39.7%

W3.8%

As 3000ppm

3.2 The method of the present invention uses OH-type (Lewatit MP 62) weakly basic anion exchangers for pre-purification. Purified W solution: W60g/lMo1.2g/lAs<1mg/l Separation of Mo using ^S2- type Lewatit MP 62 exchanger (according to Example 2) Recovered _MoS3 : Mo 40.6%W0.6%As 60ppm

Claims (6)

1. A method for preparing soda metal tungstate and/or ammonium tungstate solution from contaminated alkaline tungstate solution, the contaminated solution refers to the , niobium, titanium and molybdenum contaminated tungstate solution, the method comprises the following steps: (a) acidifying the solution to a pH value of 7-10, a large amount of impurities except molybdenum and arsenic ions are precipitated, and the precipitate is filtered; (b) carrying out the first step ion exchange process with the filtrate obtained in step (a) using a weakly basic to medium basic ion exchanger, separating the remaining impurities including arsenic but except molybdenum ions from the filtrate, and (c) treating the filtrate by adding sulfide to form thiomolybdate, and treating the filtrate containing thiomolybdate with a sulfide-type ion exchanger to remove molybdenum from the filtrate. 2. The method of claim 1, wherein the solution is acidified to a pH of 7-10 using one or more mineral acids, _CO2 and/or membrane electrolysis. 3. The method according to claim 1 or 2, characterized in that the pH value is adjusted to 8-8.5. 4. The method according to claim 1 or 2, characterized in that the solid OH type weakly basic to moderately basic ion exchanger is used to separate the remaining impurities including arsenic but except molybdenum. 5. The method according to claim 1 or 2, characterized in that a stoichiometric amount of sulfide of 3-5 times the molybdenum content is added in order to generate thiomolybdate. 6. The method according to claim 1 or 2, characterized in that the sulfide used is H ₂ S, NaHS, Na ₂ S, (NH ₄ ) ₂ S or an organic compound that can release sulfide.